关键词: GPS观测, 速度场, 地壳速度, 地壳物质东流, 连续变形, 青藏高原

Abstract: As the most prominent example of large scale continental deformation,Tibetan Plateau offers an ideal natural laboratory for quantifying such deformation and understanding the relevant dynamic processes. Global Positioning System (GPS) provides a powerful means to directly measure the kinematics of present day deformation. Our synthesis of GPS velocities from 553 stations in Tibetan Plateau and its margins quantitatively show that most of the relative India/Eurasia motion has been accommodated primarily by crustal shortening along the margins,strike slip and normal faulting in the plateau interior,and clockwise rotation around the eastern end of Himalayas. Taken 36～40mm/yr as total relative motion between India and Eurasia,the eastern Tibetan Plateau and its margins accommodates 85%～94% of the total motion,whereas western Tibet absorbs 70%～91% of total convergence and the rests are taken up by shortening across the Tianshan in the north. The NNE SSW shortening of the plateau interior is accommodated by conjugate strike slip faulting and orthogonal normal faulting,which do not require crustal thickening or thrust faulting. The eastward extrusion of Tibetan Plateau out of India's northward pass is carried out by roughly eastward flow of crustal material rather than by rigid block rotation. The flow of Tibetan crustal material rotates around the eastern Himalayan syntaxis,causing southeastward to southward and even southwestward velocities observed in southern and western Yunnan Province of China. To the east,the eastward flow of crustal material causes shortening across the eastern margin of the plateau and clockwise rotations of the region where resistance to such flow is weak. To the west,the westward motion of the western margin of the plateau is observed with only 4mm/yr slip rate. Components of velocity of Tibetan Plateau in both parallel and perpendicular directions to the relative motion between India and Eurasia can not be attributed to slips along a few faults either strike slip or thrust because of their distributed nature. Thus,the present day tectonics in the Tibetan Plateau is best described as deformation of a continuous medium,at least when averaged over distances of ～100km.

Key words: GPS measurement, velocity field, crustal velocity, eastward flow of crustal material, continuous deformation, Tibetan Plateau